1. Field of the Invention
The present invention relates to a solar power generation apparatus and a control method therefor and, more particularly, to a solar power generation apparatus capable of minimizing instances of undesired operation of an earth leakage circuit breaker, and a control method therefor.
2. Description of the Related Art
As the popularity of home solar power generation systems grows, many studies aiming at cost reduction are being made. To that same end, currently roof-integrated solar battery modules which require no frames, and non-isolated inverters (so-called transformerless inverters) are being put into practical use.
FIG. 6 shows the arrangement of a general system interconnection solar power generation system. The system interconnection solar power generation system sends power generated by a solar battery array 1 to a commercial power system 3 via an inverter 2. An earth leakage circuit breaker 4 is inserted between the inverter 2 and the commercial power system 3. When an earth leakage failure occurs at a customer's or subscriber's home, the earth leakage circuit breaker 4 completely disconnects the solar power generation system from the commercial power system 3 to prevent spread of disasters (e.g., fire).
Since solar batteries are installed outdoor across a relatively large area (e.g., about 30 m.sup.2 for a power generation capacity of 3 kW), the solar battery array 1 has a relatively large earth capacitance 5, and this may generate a leakage current which may inadvertently operate the earth leakage circuit breaker 4, as is pointed out in K. Furkawa, et al., "Transformer-less Inverter for Photovoltaic Power System", The Institute of Electrical Engineers of Japan, Industry Applications Society, National Convention, Transaction No. 77, pp. 217-220 (1996). Actually, when an earth leakage circuit breaker and, more particularly, an input earth leakage circuit breaker operates, service interruption is experienced by the customer. Even when an earth leakage circuit breaker is dedicated to an inverter for solar power generation, solar power generation is stopped by breaking operation of the earth leakage circuit breaker, resulting in a loss in the generated energy.
Takehara as one of the present inventors has disclosed, in U.S. Ser. No. 09/071,299, the relationship between the earth capacitance and the sensitivity of the earth leakage circuit breaker, with which hardly any undesired operation of the earth leakage circuit breaker occurs. Having also found as result of extensive studies that an impulse-like leakage current as shown in FIG. 2 is generated due to a variation in the earth potential of the solar battery array at the start time of interconnection of a transformerless inverter, he proposed in Japanese Patent Application No. 10-61898 that instances of undesirable operation of the earth leakage circuit breaker are eliminated by providing a potential fixing means in the transformerless inverter. With this proposal, when a transformerless inverter and an earth leakage circuit breaker form one set, operation errors of the earth leakage circuit breaker can be eliminated.
However, in a relatively large solar power generation system, a plurality of transformerless inverters may be connected to a single earth leakage circuit breaker. In this case, measures against undesirable operation of the earth leakage circuit breaker have not yet been fully explored.